Hubble's Famous M31 VAR! plate

On the night of October 5-6, 1923, Carnegie astronomer Edwin P. Hubble took a plate of the Andromeda Galaxy (Messier 31) with the Hooker 100-inch telescope of the Mount Wilson Observatory. This plate, with identification number H335H ("Hooker plate 335 by Hubble"), is famous for having led to his discovery of the first Cepheid variable star in M31, which established beyond any doubt that M31 was a separate galaxy from our own.

Shown here are three images of Plate H335H as well as three images of a similar plate, H331H, which Hubble took the night before. The letters N on Plate H335H mark Novae, stars marked by Hubble as new when compared with earlier plates. The first Cepheid variable discovered has its letter N crossed out and is marked "VAR!", showing that Hubble originally thought it was a nova, but eventually discovered that it varied in brightness like a Cepheid.

The first image of H335H shows the glass side of the photographic plate, on which Hubble marked novae and, eventually, the first Cepheid in ink. The next two images show the emulsion side of the plate at two contrasts, with Hubble's writing of plate information at the top (Plate ID, M31, 45 min exposure on plate of type Seed 30, seeing of 3+ on Mt Wilson scale, date, and hour angle of 2 hr 8 min East at the end of the exposure).

The first image of H335H shows the glass side of the photographic plate, on which Hubble marked novae and, eventually, the first Cepheid in ink. The next two images show the emulsion side of the plate at two contrasts, with Hubble's writing of plate information at the top (Plate ID, M31, 45 min exposure on plate of type Seed 30, seeing of 3+ on Mt Wilson scale, date, and hour angle of 2 hr 8 min East at the end of the exposure).

The three images of the comparison plate H331H are shown below in the same sequence. Note that the seeing during this 40 min exposure was poor ("Seeing <1"), near the bottom of the Mt Wilson scale (0-5).

COPYRIGHT: The above images are all copyright protected. Downloads for inspection, scientific and historical work are free. However, any reproduction in commercial products (including books) must be licensed by Carnegie Observatories and will be assessed a permission fee. For permission to use any of these images in a commercial product, please contact John Grula